In the 21st century, the rapid development of telecommunication technology has encouraged providers to serve the best services for their customers. They have built traffic redundancy and added more capacity. For instance, a 6G network will be deployed immediately. It needs more bandwidth in the transmission line. Currently, there is no submarine cable passing through the Southern Sea of Java. This paper considers designing an optic network that passes through the Southern Sea of Java route to back up the existing route in the Northern Sea of Java from issues such as fiber cuts, tsunami disasters, equipment issues, etc. The total number of proposed drop points was seven nodes to deliver data traffic from Singapore to Surabaya. This network will give all the Southern Java routes more bandwidth and capacity than the Northern Java Route. The proposed method uses Space Division Multiplexing (SDM) technology and is combined with Dense Wavelength Division Multiplexing (DWDM) used in Multi-Core Fiber. The link margin of the proposed network is 6 dB to anticipate losses from the fiber repair, equipment drop point, and submarine/terrestrial repeater issue. The rise time on the system was 683.42 ps using the Dispersion Compensation Module (DCM). Deployment of this backbone network can cost approximately 1 million USD for 10 years of investment, offering big capacity with low CAPEX and OPEX.